Announcements for the Department of Physics at UMBC

October 2009 Archives

October 7, 2009

Seminar: Wednesday, October 7, 2009 at 3:30 p.m.

How do we know whether to believe model predictions?

Dr. Susan Strahan
Goddard Space Flight Center

Chemistry climate models (CCMs) embody the state of our knowledge of atmospheric chemistry and physics. They are used to predict future changes in atmospheric composition and climate based on estimates of future emissions of CO2, CH4, N2O, chlorofluorocarbons (CFCs), and other trace species. Every four years, chemistry climate modeling groups participate in an international effort sponsored by the World Meteorological Organization (WMO) to predict the future state of the stratospheric ozone. 13 CCMs participated in the most recent WMO assessment and they produced a wide range of predictions for benchmarks such as the date of the disappearance of the Antarctic ozone hole and the return of northern midlatitude ozone to 1980 levels. How do we know which, if any, of the model predictions to believe?
The answer lies in the use of observations to assess the ability of CCMs to represent key aspects of stratospheric circulation and chemistry. The analyses of several decades of aircraft, balloon, and satellite trace gas observations such as O3, H2O, CH4, and N2O have identified many important transport processes in the stratosphere. We use observational analyses to derive diagnostics for stratospheric transport processes, and because of them we now understand many aspects of stratospheric circulation, e.g, the rate at which air ascends in the tropical stratosphere and the existence of transport barriers in the subtropics and polar regions. Diagnostics are applied to model simulations to assess whether models realistically represent known processes. In recent years an international group of scientist has been systematically applying a growing set of stratospheric chemistry and transport diagnostic to CCMs in order to better understand their behavior and determine model credibility. This effort is providing a rational basis for distinguishing between model predictions of the future of stratospheric ozone.

October 14, 2009

Seminar: Wednesday, October 14, 2009 at 3:30 p.m.

Interstellar Dust: The Universe through Rose-Colored Glasses

Dr. Ulysses J. Sofia
American University

Most astronomical observations are affected by interstellar dust, the submicron sized solid particles that live in the medium between stars. This is especially true as we observe increasingly distant objects with higher redshifts. The dominant method for accounting for light distortion by interstellar dust is an empirical correction which has a restricted range of validity. We are seeking to understand dust and its distorting affects in a context that is based in physics so that we may better correct for its effects on astronomical observations. We do this primarily through the study of the physical and chemical composition of dust, and radiative transfer models that relate potential dust grains to distortion effects. Data from the Hubble Space Telescope has allowed us to make great progress in this field over the past 18 years, but there are still fundamental pieces of the puzzle that do not fit together.

October 21, 2009

Seminar: Wednesday, October 21, 2009 at 3:30 p.m.

Lethal Landscapes: the Soviet-American history of plutonium, radiation and the communities that learned to love and then fight over the bomb

Dr. Kate Brown
University of Maryland Baltimore County

In 1944, brigades of construction workers, soldiers and prisoners transformed Richland, Washington from a ranch town to an ‘operators’ village’ exclusively reserved for workers at the new Hanford Engineering Works, a vast, ambling complex behind cyclone fencing that produced plutonium for the Manhattan Project. A few years later, inspired by Hanford, soldiers, prisoners and construction workers broke ground on another special city dedicated to plutonium workers. This one located in the thick, marshy forests of the southern Russian Urals. Both cities, Richland and Cheliabinsk-40*, existed to secure the secrets of plutonium. To keep the plutonium safe, plant employees were carefully-screened and closely-watched in isolated communities in remote locations. To keep the plutonium workers, engineers and scientists happy in these provincial locations, industrial leaders rewarded them handsomely and invested generously in the plutonium communities.

In short, it took a village (really a small city) to produce the few kilograms of plutonium necessary for a nuclear bomb. The cities existed for four decades in relative obscurity (Richland) or outright secrecy (Cheliabinsk-40). Chernobyl changed all that. When reactor number four blew in April 1986, it gave a pulse to anti-nuclear groups that had long demanded to know what went on behind the cyclone fencing of military nuclear installations. As American and Soviet documents were de-classified, the public learned that the plants had dumped, each day, tens of thousands of curies of radiation into rivers, air and soil. As the days had accumulated into decades, the total of spilled curies mounted into the millions and then hundreds of millions.

Since Chernobyl, the public memory of the plutonium cities has existed in a vortex of controversy. Commentators, residents, and activists characterize the plutonium cities variously—as radioactive and dangerous, or as safe and wholesome, “a great place to grow up.” People in towns surrounding the plutonium cities filed lawsuits for damage from what they charged were radiation-related health problems. Meanwhile, many residents in the cities fought against acknowledging a connection between the plutonium plants and local health problems.

Brown argues that the contentious legacy of the plutonium cities derive from the fact that the cities were built as model modern communities with novel new security regimes. Meanwhile radiation was also a modern contaminant--undetectable without sensitive equipment and the source of illness only after long latency periods. In short, the incongruity of the comfortable and thriving plutonium cities against an invisible, radioactive geography enabled the tragedy of massive environmental contamination, enabled too the personal tragedies of contaminated bodies to go unnoticed and unheeded for decades and remain controversial to this day.

October 28, 2009

Seminar: Wednesday, October 28, 2009 at 3:30 p.m.

The Fermi Gamma-Ray Space Telescope and the Search for Dark Matter

Yvonne Edmonds
Stanford University

The Fermi Gamma-Ray Space Telescope launched in June 2008 opening a new window on the highest energy sources in the universe. I will give a brief overview of how Fermi’s primary instrument, the Large Area Telescope (LAT), detects gamma-rays and its topics of study. One of the most exciting possibilities for the Fermi-LAT is the indirect detection of dark matter. Well-motivated and popular dark matter theory assumes that a significant component of dark matter is Weakly Interacting Massive Particles (WIMPs). I will go over WIMP basics, and the strategies involved in dark matter searches. Finally, I will talk about my work on the possibility to observe gamma lines from WIMP annihilation into gamma-gamma and gamma-Z final states. Detection of these lines would give convincing evidence for the existence of WIMPs and the WIMP mass.